Thermal valve



July 9, 1968 F. KELLY 3,391,728

THERMAL VALVE Original Filed July 5, 1964 HEA TSOURCE-M E U TE 6 77C SOLDER-l6 BE/PYLL/A WAFER-l5 E U TE 6 77C SOLDER-l/ P-N JUNC T/ON-IO EUTECT/CSOLDER-l? co /wev? PLA TE-l8 EU TECT/C 50L DER-l9 HER/M5776 TERMINAL-12 HEATS/'20 g 0.0. AMPLIFIER r/igfiuo c gugg 23 22 20 MN HEAT HEAT SOURCE zo S/NK SPIN AXIS Fig.4.

C0 UNDER PRESSURE mmvron: FRANKLIN a KELLY,

United States Patent 3,391,728 THERMAL VALVE Franklin Kelly, Long Beach, Calif., assignor to TRW Inc., a corporation of Ohio Original application July 3, 1964, Ser. No. 380,136, now

Patent No. 3,302,703, dated Feb. 7, 1967. Divided and this application Aug. 22, 1966, Ser. No. 574,222

4 Claims. (Cl. 16532) ABSTRACT OF THE DISCLOSURE A heat valve is formed in a gap between two surfaces at different temperatures by the use of a liquid thermal conductor which is controlled to fill the gap to varying levels and hence varying the conduction of heat across the gap. The valve uses a gas under pressure to fill the gap and a flexible reservoir filled with the liquid conductor and controlled by a bimetallic strip.

This invention relates to a thermal valve and more particularly to a controllable thermal valve in which the thermal conductivity can be varied upon command.

This application is a division of copending application Ser. No. 380,136 filed July 3, 1964, nOW Patent No. 3,302,703, patented Feb. 7, 1967.

In this invention there is disclosed two different embodiments, one electrical in nature and the other mechanical in nature in which the thermal conductivity is variable thereby providing a measure of control over the flow of heat from a first member to a second member. This invention is not to be confused with refrigeration or cooling techniques in which heat is pumped from one area to another. The pumping systems may use the so-called Peltier eifect which is more akin to a heat pumping arrangement. In this invention, it is possible, upon command, to provide a path of either low or high thermal conductivity between a first member and a second mem ber.

In one embodiment of this invention, a transistor or preferably a large semiconductor diode is connected between 21 heat source and a heat sink and in the electrical forward direction measured from the heat source to the heat sink. In order to provide electrical isolation, a material of high thermal conductivity and high dielectric constant such as beryllia is connected in series with the leads from the diode. It was discovered that reverse biasing the diode provided a thermal barrier between the heat source and the heat sink Whereas a forward bias on the diode provided a heat path of high conductivity between the heat source and the heat sink. By making the biasing means responsive to the temperature of the heat source or the heat sink, it is possible to control and maintain the temperature of the heat source at some predetermined value.

The second embodiment for controlling thermal conductivity between members represents a mechanical implementation of the same principles of the disclosed invention. In this embodiment, a heat source and a heat sink are separated by a gap which is substantially filled with a gas having a low thermal conductivity such as CO gas. A liquid thermal conductor, such as mercury, is inserted in the gap which is sealed at both ends thereby placing the gas under pressure. A reservoir in the form of a bellows holds the major supply of the mercury in definite proportions whereby pressure on the bellows causes the mercury to substantially fill the gap and thereby provide a low thermal path across the gap. With no external pressure on the bellows, the mercury is forced substantially completely into the bellows by the gas under c CC pressure thereby providing a gap filled with a thermally insulating gas between the heat source and the heat sink.

Further objects and advantages of the present invention will be made more apparent by referring now to the accompanying drawings wherein:

FIG. 1 is a cross section of a semiconductor diode constructed according to the teachings of this invention;

FIG. 2 is a block diagram illustrating a transistor application of the thermal valve;

FIG. 3 is a schematic diagram illustrating how a junction diode may be used according to the teachings of this invention; and

FIG. 4 is a diagram illustrating a mechanical implementation of the invention.

Referring now to FIG. 1, there is shown in cross section a PN junction 10 having a surface: area determined by the thermal resistance required. Bonded to one side of the junction 10 is a eutectic solder 11 which forms a basis for connecting a biasing voltage through a hermetically sealed terminal 12 to an internal lead 13 which connects the terminal 12 to the eutectic solder 11. The PN junction. The opposite end of the P-N junction 10 14 by a beryllia wafer 15 which has a high thermal conductivity and a high dielectric constant. The opposite end of the beryllia wafer 15 contains a eutectic solder 16 to which the heat source 14 is attached and which insures a low thermal path from the heat source to the PN junction. The opposite end of the PN junction 10 is bonded to eutectic solder 17 to which a copper plate 18 is attached to thereby insure good electrical and thermal contact to the PN junction. The opposite end of the copper plate 18 is connected to eutectic solder 19 to which a heat sink 20 is attached. A lead can be attached to the eutectic solder 19 which will thereby provide a circuit for the biasing voltage through the eutectic solder 19, the copper plate 18 and the solder .17 to the PN junction 10. The circuit for the terminal 12 comprises internal lead 13, and solder 11 to the PN junction 10. In the usual case, the heat sink 20 could be grounded which would act as one terminal for the system. For those systems requiring both terminals to be insulated from the heat source 14 and the heat sink 20, it is only necessary to interpose a beryllia wafer between the eutectic solder 19 and the heat sink 20 and connect the second terminal to the eutectic solder 19. These insulating techniques are well known in the art and are considered ancillary to the disclosed invention.

Referring now to FIG. 2, there is shown in block form a system concept using a transistor having an emitter 20a, base 2% and a collector 20c. A heat source 14 is illustrated as being mechanically and thermally connected to a beryllia wafer 15 which is in turn mechanically and thermally connected to the emitter 20a. The collector 200 is mechanically and thermally connected I to a second beryllia wafer 21, the other side of which is mechanically and thremally connected to a heat sink 20. A pair of leads 22 and 23 are electrically attached to the emitter 20a and the base 20b and are connected to a biasing means identified as a DC amplifier 24. A suitable thermocouple 25 arranged to detect temperature fluctuations in the heat source 14 is connected in a driving relationship with the DC amplifier 24 so as to control the biasing of the PN junction 10 whenever the temperature of the heat source 14 exceeds predetermined limits. In this manner, the thermocouple 25 is made responsive to the temperature difference between the heat source 14 and the heat sink 20 to thereby control the thermal conductivity of the PN junction 10. Depending on the needs of the system and the application of the thermal valve, additional thermocouples may be connected to the heat sink for controlling the DC amplifier in combination with 3 the thermocouple or as a sole means of controlling the temperature of the heat sink 20.

Referring now to FIG. 3, there is shown a schematic diagram of a manually operated circuit for achieving the biasing volt-age capable of varying the biasing conditions on a diode from a forward direction to a reverse biased direction. There is illustrated, batteries 26 and 27 connected in series with the resistance portion of a potentiometer 28. The operating terminal 29 of the potentiometer is connected to one terminal of a diode 35 represent ing a PN junction. The opposite terminal of the diode is connected intermediate the connection between batteries 26 and 27. A review of the circuit will show that whenever operating arm 29 is centrally located in the potentiometer 28 that a zero potential will exist across the diode 30. It can be shown further that moving the operating arm 29 in the direction of battery 26 will make the arm 29 positive and hence make the cathode portion of diode 30 positive with respect to the anode. Similarly, moving the operating arm 29 in a direction of battery 27 will make operating arm 29 negative and hence an opposite biasing polarity will be presented across diode 36. It is well known that approximately 0.6 volt across a silicon diode in the direction of current flow will bias the diode in a forward direction and according to the teachings f0 this invention will raise the thermal conductivity to thereby permit passage of heat. Similarly, it has been discovered that reverse biasing the diode will lower the thermal conductivity of the diode thereby presenting a thermal barrier to the passage of heat. As mentioned previously, there is no heat pumping effect associated with this invention and as a result once the diode is biased in the forward direction, heat will flow from the higher temperature to the lower temperature but not from the lower temperature to a higher temperature as is associated with so-called pumping techniques.

Referring to FIG. 4 there is shown a mechanical embodiment of a thermal valve capable of varying the thermal conductivity from a heat source 11 to a heat sink 20. The heat source 14 and the heat sink 20 are located in close proximity to each other so as to define an interface which is substantially filled with a gas having a substantially low thermal conductivity such as CO One end of the interface is sealed by means of a sealing device 31 which provides a reservoir arrangement for the gas. The opposite end of the interface is sealed by means of a bellows arrangement 32 which contains a liquid thermal conductor such as mercury. The bellows is of such a size that the pool of mercury is capable of being stored in the bellows as a reservoir when the bellows 32 is fully extended. Pressure on the bellows will cause the mercury to be forced into the interface between the heat sink and the heat source thereby displacing the gas into its reservoir 31. Pressure on the bellows 32 is controllable by means of an arm 33 having an adjustable spring 34 at one end and being pivotally connected at the other end on the heat source 14. A bimetallic strip 35 attached to the arm 33 and held in thermal contact with the heat source 14 is arranged to move the arm 33 in response to the temperature of the heat source 14. A button 36 attached to the arm 33 contacts the bellows 32 and thereby provides the necessary pressure and movement against the bellows 32 in response to the movement of arm 33 as determined by the temperature of the heat source 14. In operation and depending upon the adjustment of the spring 34, a low temperature in the heat source 14 will cause the arm 33 to move away from the bellows 32 thereby causing the gas under pressure in the container 31 to push the mercury in the interface back into the bellows 32 which thereby provides a high resistance thermal path in the inerface between the heat source 14 and the heat sink 20. Conversely, high temperature in the heat source 14- will cause the arm 33 to bend inwardly so as to exert a pressure on the bellows 32 thereby forcing the mercury into the interface and thereby presenting a thermal path having a high thermal conductivity between the heat source 14 and the heat sink 20. The disclosed device is capable of working in a gravity free environment, by providing an artificial gravity to make certain the mercury remains in the bellows 32. In such an application the thermal switch can be positioned with respect to the spin axis as shown.

This completes the description of the embodiments of the invention illustrated herein, however, many modifications and advantages of this invention will be apparent to those skilled in the art. For example, in both embodiments it is recognized that heat leakage appears between the heat sink and the heat source must be guarded against in order to obtain the efliciencies inherent in the disclosed invention. In the mechanical embodiment, it is recognizcd that both the bellows and the gas reservoir must be thermally insulated from both the heat sink and the heat source to prevent parallel thermal paths. These techniques are certainly within the skill of knowledgeable persons skilled in the art. Accordingly, it is desired that this invention not be limited to the particular details of the embodiment disclosed herein, except as defined by the appended claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In combination,

a heat source and a heat sink separated from each other by liquid thermal conductor under pressure contacting said heat source and said heat sink,

and means responsive to the temperature of said heat source for physically controlling the pressure on said liquid thermal conductor whereby reduced pressure causes said liquid thermal conductor to be removed from the interface between said heat source and said heat sink.

2. A combination according to claim 1 in which a liquid metal is contained within a sealed enclosure including a bellows, and in which a temperature sensitive arm contacting said bellows causes said pressure.

3. In combination,

a heat source and a heat sink in close proximity to each other thereby defining an interface,

said interface being sealed and filled as one end with a gas under pressure having a substantially low thermal conductivity,

a bellows arrangement sealing the opposed end of said interface and being filled with a liquid thermal conductor capable of filling said interface and maintaining the pressure on said gas and means responsive to the temperature of said heat source for controlling the pressure on said liquid thermal conductor whereby the amount of conductor in said interface is varied and the net thermal conductivity between said heat source and said heat sink is controlled.

4. A combination according to claim 3 in which said liquid thermal conductor is mercury.

References Cited UNITED STATES PATENTS 2,363,375 11/1944 Wild 16'596 X 3,062,507 11/1962 Andrus 104 3,167,159 1/1965 Bovenkerk 16596 X 3,225,820 12/1965 Riordan 16532 X 3,229,755 1/1966 Komarow 16532 ROBERT A. OLEARY, Primary Examiner.

A. W. DAVIS, Assistant Examiner. 

